73997-39-4Relevant articles and documents
Catalysis of the Reversible Elimination Reactions of Substituted N-(β-Phenylethyl)quinuclidinium Ions in Aqueous Solution
Alunni, Sergio,Jencks, William P.
, p. 2052 - 2060 (2007/10/02)
The rate constants for elimination reactions of substituted N-(β-p-nitrophenylethyl)quinuclidinium ions induced by hydroxide ion in water at 25 deg C show only a small sensitivity to the pKa of the leaving quinuclidine, with βlg = -0.18.The primary isotope effect is kH/kD = 8.5 and the secondary solvent isotope effect is kOD/kOH = 1.55 for the quinuclidine derivative.The rates of these elimination reactions are comparable to or faster than that of 2-p-nitrophenylethylbromide.The reaction is readily reversible in quinuclidine buffers and the rate constants of the addition reaction to p-nitrostyrene show a large dependence on the pKa of substituted quinuclidines with βnuc = 0.69; the equilibrium constants in the elimination direction follow βeq = -0.89.The addition reaction shows general acid catalysis by protonated quinuclidines and the elimination reaction shows general base catalysis, with a Broensted coefficient of β = 0.68 for elimination from the diazabicyclobutane derivative.Elimination reactions from the corresponding phenyl compounds are ca. 103 slower and show a more negative value of βlg = -0.35 in water at 40 deg C; in EtONa/EtOH the value of βlg is -0.28.The change in βlg for the phenyl compounds corresponds to a negative structure-reactivity coefficient pyy' = βlg/-? = p/-pKlg, consistent with the expected E2 mechanism for the phenyl compounds.However, it is uncertain whether the p-nitrophenyl compounds react by an E2 or an irreversible E1cB mechanism.
